Clamp for printing cylinder



Oct. 16, 1956 K. KOWALSKY ET AL 2,766,689

CLAMP FOR PRINTING CYLINDER Filed Jan. 4, 1955 INVENTOR.

'CLAlVIP FOR 2' .l" G CYLINDER This invention relates to a new and improved clamp for securing one end of a stencil or other flexible printing sheet to a printing cylinder of a stencil duplicator or other printing machine.

One principal object of the invention is to provide a clamp which will exert extremely heavy pressure on the end of a stencil and thereby prevent ink from being squeezed out from under the end of the stencil by the pressure of the impression roller during duplicating operations.

Another object is to provide an improved cylinder clamp which provides great clamping pressure, yet is extremely easy to open and close.

A further object is to provide an improved cylinder clamp which is irreversible in the sense that it cannot ordinarily be opened by outward force on the member to clamp the flexible printing sheet against the printing cylinder.

Further objects and advantages of the invention will appear from the following description, taken with the accompanying drawings, in which:

Figure 1 is a fragmentary cross-sectional view of an exemplary stencil duplicating cylinder provided with a stencil clamp constituting an illustrative embodiment of the invention, the view being taken generally on a line indicated as 11 in Fig. 4;

Fig. 2 is a view similar to Fig. 1 showing the clamp in open position rather than in closed position as in Fig. 1;

Fig. 3 is a considerably enlarged fragmentary crosssectional view showing the engagement between the clamp and the stencil;

Fig. 4 is a fragmentary broadside view of one end of the cylinder of Fig. 1, partly in section generally along a line 4--4 in Fig. 1;

Fig. 5 is a fragmentary sectional View taken generally along a line 55 in Fig. l; and

Fig. 6 is a fragmentary sectional view taken generally along a line 6-6 in Fig. 2.

, If the drawings are considered in greater detail, it will be seen that they illustrate a printing cylinder 10 which in this instance constitutes the stencil carrying drum of a stencil type duplicator. However, it will be appreciated that in some cases the invention may be applicable to other types of printing machines. The illustrated stencil drum 19 comprises a cylindrically curved stencil supporting member in the form of a diaphragm 12 formed with a plurality of apertures 14 for feeding ink from a reservoir 16 to an ink pad 18 wrapped around the'outside of the diaphragm. A flexible printing sheet in the form of a stencil 20 is adapted to be wrapped around the diaphragm 12 over the ink pad 18. The diaphragm 12 and the reservoir 16 are supported between a pair of end plates 22 having inturned peripheral flanges 24.

It will be seen that the end of the diaphragm 12 is bentinwardly to define an anvil 26 against which the end of the stencil 20 may be clamped. It has been found that it is highly desirable to clamp the tail or trailing tates Patent edge of the stencil sheet against the cylinder with great force in order to prevent ink from being squeezed out from under the end of the stencil by the rolling action of the impression roller on the duplicator. At the same time, it is equally desirable to provide a tail end cylinder clamp which is easy to open and close. These advantages are combined in the clamping mechanism now to be described.

To clamp the end of the stencil 20 against the anvil 26, the illustrated cylinder 10 is provided with a movable clamping member in the form of an elongated plate or bar 28 which, as shown, is cylindrically curved and is adapted to occupy a closed position generally flush with the outer surface of the cylindrical diaphragm 12. On one longitudinal edge, the clamping plate 28 is provided with a beveled or inclined clamping surface 30 defining a tapered clamping edge portion 32 on the plate. As shown, the clamping surface 30 is inclined inwardly at an acute angle to the outer surface of the plate 28 so as to recede from the clamping anvil 26. In this way, the pressure exerted by the clamping plate 28 is concentrated adjacent the extreme outer edge of the tapered portion 32. However, the tapered edge portion 32 is formed with a rounded nose 34 and hence will not cut the stencil.

The clamping plate 28 is mounted for swinging movement on a pair of arms 36 which are rotatably supported on pivots 38. Mounting plates 39 are secured to the cylinder end plates 22 to support the pivots 38.

To provide clamping action, the clamping plate 28 is provided with camming means, comprising in this instance a pair of cams 40 formed integrally with the clamp supporting arms 36. Each of the illustrated cams 40 has a steeply inclined wedge portion 42 which joins at one end with a generally circular portion 44. A great mechanical advantage is afforded by providing a member 46 which is movable into wedging relation with the Wedge portion 42 of the cam 46. In this instance, the member 46 consists of a roller mounted on the outer end of an actuating arm 48 which is supported by a pivot 50a secured to the mounting plate 39. A spring 50 is provided to act on the arm 48 and thereby bias the roller 46 against the cam 46. It will be observed that the arcuate path of the roller 46 intersects the wedge portion 42 of the cam at a small acute angle. The wedging action between the roller 46 and the wedge portion 42 results from this angular relationship. Because of the mechanical advantage afforded by the wedging action, the force applied by the roller 46 to the cam 40 is multiplied with respect to the force exerted by the spring 50 on the arm 48. Moreover, it will be observed that the line of action of the force exerted by the roller 46 on the cam 40 is spaced a substantial distance outwardly from the pivot 38. Accordingly, the roller provides a heavy clamping torque on the clamping plate 28.

In order that the clamp 28 may be easy to open and close, separate means are provided for withdrawing the actuating member 46 from the wedge portion 42 of the cam. To this end, the stencil cylinder 10 is provided with a pair of manually operable levers 52 at opposite ends of the cylinder. In this instance, the levers are mounted on the same pivots 38 which support the clamp 28. An elongated bail rod 54 extends between the levers 52 and serves as a common handle.

For the purpose of moving the rollers 46 away from the wedge cam portions 42, the levers 52 are formed with respective integral clamp releasing cams 56 which have a gradual outward inclination. As the levers 52 are swung clockwise, as viewed in Figs. 1 and 2, the rising cam portions 56 engage the rollers 46 and swing them away from the wedge portions 42. This relieves the a nesia s3 clamping force on the clamp 28. Each of the releasing cams 56 has a high point 58 corresponding in radius to the circular portion 44 of the actuating cam 40. Thus, the releasing cam 56 swings the roller 46 a distance such that the circular portion 44 of the actuating cam can move past the roller. 4 i i v In order to swing the clamp 28 to its open position, an arm or finger 60 is formed on each of the releasing levers 52 and is adapted to engage the underside of the clamping bar 28, after the roller 46 is moved away from the wedge cam portion 42. As the fingers 6i) swing open the clamp 23, the arcuate cam portion 44 moves past the roller 46.

'The clamp'may be closed simply by pushing inwardly on the clamping plate 28. The clamping plate inturn pushes the fingers 60 inwardly and thereby swings the releasing levers, 52 toward their initial positions. As the clamping. plate 28. is swung inwardly the roller 46 rides along the arcuate cam portion 44 until it reaches the steeply inclined portion 42, whereupon the roller forcibly closes the clamp so as to press the stencil 20 and the underlying ink pad 18 against the anvil 26, as. shown in Fig. 3.

It will be understood that the gradually rising releasing cam 56 provides a favorable mechanical advantage for. swinging the actuating. roller 46 away from the vedge portion, {2 and thereby releasing the clamping pressure on the clamping plate 28. Accordingly, the clamp is easily opened, no matter how small the wedgi ng angle is made between the arcuate path of the roller andfth wedge portion 42. Thus, the wedging angle may be made so small that the Wedge clamping action is irreversible. With irreversible clamping action, no amount of force on the clamping plate 28 will open the clamp." Thus, the tail end of the stencil 20 will remain firmly secured to the cylinder under all operating conditions. Moreover, the clamping force exerted by the plate 28 on the stencil may be made adequate to prevent outward leakage of ink under the stencil.

Although the clamp of the present invention finds its most advantageous application as a tail clamp for stencil printing sheets, it may also be employed to clamp the head end of the stencil, and in some cases may be advantageons for securing other types of flexible printing sheets to. a printing cylinder.

Various modifications, alternative constructions and equivalents may be employed without departing from the true spirit 'andscope of the invention as exemplified in.

the foregoing "description and defined in the following Claims, H v. Weclaim:

1'. In a printing cylinder having a cylindrically curved.

member for supporting a flexible printing sheet, the com bination comprising anvil 'means at one end of said cylindrically curved member for supporting one end of the printing sheet, a clamping member s'wingably mounted on said cylinder and movable toward said anvil means to. clamp. theend. ofthe printing sheet therebetween, a steeply. inclined wedge cam on said clamping member, an actuating member movable along a path, intersecting said wedge cam ata smallwedging angle, a spring biasing said actuating member alongsaid path toward said wedge cam, a manually operable releasing lever swingably mounted on said cylinder, a gradually rising cam on said lever and movable into engagement with said actuat-l ing. member to move the same against the biasing action of said spring away from said wedge cam, and an arm on said. lever movable into engagement with said clamp: ing member after said actuating member has beenemoved awayfrom said wedge cam for swinging said clamping member away from said anvil means. 4

2. In a printing cylinder having a cylindrically curved member. for supporting a flexible printing sheet, the combination comprising means defining a clamping anvil adjacent one end of said cylindrically curved member to provide underlying support for one end of the flexible printing sheet, a clamp pivotally mounted on said cylinder and having an elongated clamping member with one longitudinal edge movable toward and away from said anvil to clamp the printing sheet therebetween, a cam on said clamp and having a steeply inclined wedge portion and an adjacent generally circular portion, an actuating member movable generally radially relative to said cam into and out of wedging relation with said wedge p io si t m n iasin sai a uatin rnember into engagement with said cam to swing saidclamping member forcibly against said anvil by wedging action with aid we g ps i a nua y operable rele s means having an element for moving said actuating member away from said wedge portion, said releasing means having a second element for thereupon swinging said clamp away from said anvil, said generally circular portion of said cam thereby being moved into operative relation with said actuating member, said clamp being adapted to be closed by manually swinging the same toward said anvil to reset said releasing means and allow said actuating member to return into wedging relation with said wedge portion.

3. Ina printing cylinder having a cylindrically curved member for supporting a flexible printing sheet the combination comprising means defining a clamping anvil adjacent one end of said cylindrically curved member to provide underlying support for one end of the flexible printing sheet, a clamp pivotally mounted on said cylinder and having an elongated clamping member with one longitudinal edge movable toward and away from said anvil to clamp the printing sheet therebetween, a cam on each end of said clamp and having a steeply inclined wedge portion and an adjacent generally circular portion, an actuating member movable generally radially relative to each cam into and out of wedging relation with said wedge portion, resilient means biasing each actuating member into engagement with said cam to swing said clamping memberforcibly against said anvil by wedging action with said wedge portion, manually operableireleasing levers having a bail rod therebetween, each lever having anelement for moving one actuating member away from said wedge portion, each releasing lever having a second element for thereupon swinging said chmpaway from said anvil, said generally circularportion of said cam therebybeing moved into opera tive: relation with said actuating member, said'clamp being adapted to be closed by manually swinging the same toward said anvil to reset said releasing levers and allow saidi actuating member to return into wedging relation withfsaidwedge portion.

4. In a printing cylinder having a cylindrically curvedsuntaceefon supporting a. flexible printing sheet, the combination comprising means defining a clamping anviladjacent; one end'. of said cylindrical memberto provide underlying support for one end of the flexible-printing sheetya clamp, pivotally mounted: on said cylinder and having an elongated. clamping member with onelongitudinalg-edge movable toward and away from said an vil to clamp the; printing sheet therebetween, a cam on said clamp and, having a. steeply, inclined wedge portion and an adjacent generally circular portion, an.v actuat-v ingmember. movable generally radially. relativeto saidcaminto and out of. wedging relationwith said wedge portion, resilient means biasing; said actuating member toz n aaement With said cam,- to swing saidclarnping member forcibly against; said anvil by. wedging action Withsaid wedgeportion, manually. operable releasing.

means havinga releasing cam for moving said actuating member away from said wedge portion, saidreleasingi means having an: element for thereupon swinging: said" ed re cl sed; y. manua y wia in e a tQWRIdi said anvil to reset said releasing means and allow said actuating member to return into wedging relation with said wedge portion.

5. A cylinder clamp for securing one end of a flexible printing sheet to a printing cylinder, said clamp comprising an elongated clamping bar having one edge adapted to clamp a flexible printing sheet against a printing cylinder, means pivotally supporting said clamping bar for swinging movement toward and away from the flexible printing sheet, an actuating cam connected to said clamping bar and having a steeply inclined wedge portion, an actuating arm having a roller thereon engaging said cam and movable into wedging relation with said wedge portion to clamp said bar against the printing sheet with a great mechanical advantage, a spring biasing said arm for forcibly engaging said roller with said cam, a pivotally mounted releasing lever having a manually operable element thereon, said releasing lever having a releasing cam thereon engageable with said roller by swinging movement of said releasing lever in one direction for moving said roller away from said wedge portion, a finger on said releasing lever for engaging said clamping bar and moving the same away from the printing sheet as an incident to further movement of said releasing lever in said direction, said actuating cam having a generally circular portion adjacent one end of said wedge portion for engaging said roller when said clamping bar is moved away from the printing sheet, said clamp being adapted to be closed by manually swinging said clamping bar toward the printing sheet so as to engage said finger, withdraw said releasing cam from said roller, and swing said actuating cam until said roller engages said wedge portion and forcibly seats said clamping bar.

6. In a printing cylinder having a cylindrically curved member for supporting a flexible printing sheet, the combination comprising means defining a clamping anvil adjacent one end of said cylindrically curved member to provide underlying support for one end of the flexible printing sheet, a clamp pivotally mounted on said cylinder and swingable toward and away from said anvil to clamp the printing sheet therebetween, a cam on said clamp and having a steeply inclined wedge portion rising to an adjacent generally circular portion, an actuating member movable generally radially relative to said cam into and out of wedging relation with said wedge portion, resilient means biasing said actuating member into engagement with said cam to swing said clamp forcibly against said anvil by wedging action with said wedge portion, manually operable releasing means for retracting said actuating member away from said wedge portion, said clamp thereupon being swingable away from said anvil, said generally circular portion of said cam thereby being moved into operative relation with said actuating member to retain said actuating member in retracted position, said clamp being adapted to be closed by manually swinging the same toward said anvil to return said wedge portion into wedging relation with said actuating member.

Brasseur Nov. 16, 1926 Dressel et a1. July 14, 1953 

